Method for forming an electrode layer by a laser flow technique

ABSTRACT

A method for forming an electrode wiring by laser flowing a semiconductive wafer having an intermediate insulating film, a contact hole in the film and an Al alloy film serving as a wiring metal film and formed over the intermediate insulating film and the contact hole, which method comprises forming an anti-reflective film on the Al alloy film, irradiating individual IC chips on the semiconductive wafer with a laser beam in such a way that the beam size is larger than an IC chip size and the laser beam is irradiated on an adjacent IC chip in a subsequent irradiation cycle as superposed on a grid line of the semiconductive wafer which has been irradiated with the first laser beam irradiation at least partly, thereby causing the Al alloy film to be metal flow to fill the contact hole. The thus flown Al alloy film on which the anti-reflective film has been formed is subjected to patterning to form a wiring layer.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention relates to a method for forming an electrode layer andmore particularly, to a method for forming an Al layer by the use of alaser flow technique.

2. Description of The Prior Art

A typical known wiring method is described with reference to FIGS. 4 and5 wherein FIGS. 4(a) and 4(b) are, respectively, illustrative viewsshowing the formation steps using a laser flow technique and FIG. 5shows a beam pattern in the laser flow process.

As is particularly shown in FIG. 4(a), a field oxide film 2 is formed ona non-active region of a Si substrate 1 by the LOCOS method. A gateelectrode 3 is the formed on an active region of the Si substrate 1.Source and drain diffusion layers 4 are formed on the surface of the Sisubstrate 1 at opposite sides of the gate electrode 3. Subsequently, aBPSG film 5 serving as an intermediate insulation film is deposited overthe entire surface of the Si substrate 1 on which the source draindiffusion layers have been formed. In order to permit contact with thesource drain diffusion layers, contact holes 6 are formed through theBPSG film 5 by the RIE method. Over the entire surface of the BPSG filmwhich has been provided with the contact holes 6, there are successivelydeposited by sputtering an Al-Si film 7 having a Si content of 1% and anamorphous Si film 8 used as an anti-reflective film. Since the films 7and 8 are difficult to form in the contact holes 6 by sputtering, thefilm thicknesses become smaller than in other portions.

Thereafter, an XeCl excimer laser with a wavelength of 308 nm radiatesover the IC chip formed on the Si substrate 1. The laser beamirradiation is effected by scanning or directing the beam having a givendiameter in the manner shown in FIG. 5. At the time, the beam isprojected or directed in such a way that when an adjacent portion isthen irradiated, once irradiated portion of the IC chip is againirradiated with the beam in a next cycle at 10 to 50% of the beam size.In other words, while the beam is directed along one locus, it overlapsonto an adjacent path, which path will be more directly radiated at alater time, or will have already been irradiated.

As a result of the irradiation, the Al-Si film 7 flows to fully fill thecontact holes 6 therewith as shown in FIG. 4(b). Subsequently, the Al-Sifilm 8 is subjected to patterning to form an Al wiring layer on thecontact holes 6. It will be noted that during the metal flow (of film7), the amorphous film 8 is molten in the Al-Si film.

In the case of the laser beam irradiation as set out above, it isnecessary to superpose the laser beams every irradiation cycle whereinsuperposed portions of the respective IC chips suffer additional lightenergy as compared with portions where not irradiated twice by thesuperposition. In the superposed portions, the Al-Si film 7 abnormallygrows with respect to the grain size. In a worst case, the Al-Si film 7may be lost by evaporation or separation. Thus, the problem arises thatthe elements formed in the IC chip will be greatly damaged.

Moreover, since the amorphous Si film 8 is molten in the Al-Si film,there is the tendency that the resistance of the Al wiring 7 willincrease, or Si nodules will increase in size and number. This leads tothe problem that the wiring lifetime is considerably shortened.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method for forming anelectrode wiring layer or pattern wherein the damage to elements in ICchips as will be caused by the laser beam superposition can besuppressed to a significant extent.

Another object of the invention is to provide a method for forming anelectrode wiring layer or pattern wherein the lowering in quality of thewiring film as will be caused by the residue of an amorphous Si from ananti-reflective film can be prevented.

According to the present invention, there is provided a method forforming an electrode wiring pattern which comprises:

depositing an intermediate insulating film on given portions of asemiconductor wafer and making at least one contact hole in theintermediate insulating film;

depositing an Al alloy film over the at least one contact hole and theintermediate insulating film;

depositing an anti-reflective film on the Al alloy film, thereby forminga plurality of IC chips on the semiconductor wafer, the IC chips beingseparated from one another through a grid line region;

irradiating the semiconductive wafer having the plurality of IC chipsone by one with a laser beam which is so controlled as to have a beamsize larger than a chip size and to cause a superposed portion of thebeam to be set on a grid line region of the semiconductor wafer untilthe Al alloy film suffers the metal flowing effect, thereby filling theat least one contact hole with the Al alloy film; and

selectively etching the anti-reflective film and the Al alloy filmsuccessively thereby forming on the at least one contact hole an Alwiring pattern having the anti-reflective film thereon. The laser beamirradiation and the selective etching procedures set forth above arerepeated on all the IC chips on the semiconductive wafer, therebyforming an electrode wiring on the respective IC chips.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are, respectively, illustrative views of metalflowing steps using a laser beam according to the method of theinvention;

FIG. 2 is a schematic view of a laser beam irradiation pattern accordingto the method of the invention;

FIG. 3 is a graphical representation of the light reflectance inrelation to the variation in thickness of an anti-reflective film;

FIGS. 4(a) and 4(b) are, respectively, illustrative views of metalflowing steps using a laser beam according to a known method;

FIG. 5 is a schematic view of a laser beam pattern according to theknown method; and

FIG. 6 is an illustrative view of an apparatus for causing of metal flowon a semiconductor wafer with a laser beam.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made to the accompanying drawings and particularly, toFIGS. 1 through 3 and 6 illustrating one embodiment according to theinvention.

FIGS. 1(a) and 1(b) show a process to fabricate an Al alloy wiringpattern on an IC chip, FIG. 2 shows a beam pattern, and FIG. 3 shows agraph of light reflectance in relation to the variation in thickness ofthe anti-reflective film.

FIG. 1(a) shows a semiconductor wafer 11 such as a Si substrate having afield oxide film 12 formed on a non-active region of the wafer 11 by aLOCOS method. On (or just above, as shown) a given portion of an activeregion of the wafer 11 is a gate electrode 13. Subsequently, sourcedrain diffusion layers 14 are formed on the surface of the Si substrate11 (adjacent) at both sides of the gate electrode 13. In this state, aBPSG film 15 serving as an intermediate insulating film is depositedover the entire surface of the Si substrate 11 where the film 12 and thelayers 14 have been formed. Thereafter, the BPSG film 15 is selectivelyremoved by etching to form contact holes 16 by the RIE (reactive ionetch) method so that the source drain diffusion layers 14 are exposed.Then, a refractory metal layer 17, such as a Ta-Si film as a barriermetal, with a thickness of, for example, 1000 angstroms and an Al alloyfilm 18, such as an Al-Si film, with a thickness of, for example, 0.6 μmare successively deposited over the entire surface of the Si substrate11 as shown. A tungsten (w) film 19 used as an anti-reflective film isformed on the Al alloy film in a thickness of not less than 20 nm, forexample, in a thickness of 300 angstroms. Thus, an IC chip die is formedon the Si substrate or wafer 11. In this manner, a plurality of IC chipsdies are formed on the substrate 11 although not particularly shown inthe figures.

In the practice of the invention, the thus processed semiconductor wafer11 is heated with a laser beam.

FIG. 6 schematically shows a laser beam irradiating apparatus. In thisfigure, the semiconductor or Si wafer is indicated at 31. The Si wafer31 is mounted on a stage 33 of an XY table provided in a chamber 32 andheated with a heater 34. The heating temperature should be higher than arecrystallization temperature of Al, which may be in the range of from150° to 200° C. although depending on the manner of formation of the Alalloy film 18, but within a range where no influence in given on theelements formed on the wafer 31. Generally, the temperature isapproximately 300° C. The chamber 31 should be in an atmosphere of aninert gas or should be reduced to a pressure of 10⁻³ Torr., by the useof a vacuum pump (not shown). By this, the tungsten film 19 is preventedfrom oxidation when heated.

The wafer 31 in a heated state is subjected to irradiation with a laserbeam from an XeCl laser 35. The laser beam used may be one which has afrequency of 100Hz, the pulse width number of 10 nsec. and a wavelengthof 308 nm. The laser beam is reflected at a half mirror 36 and passedthrough an optical system 37 to irradiate the surface of the wafer 31.The optical system 37 includes a lens 38 and an aperture 39 resemblingthe shape of the respective IC dies, and is used to control the laserbeam with a size A×B discussed hereinafter and a beam energy of 2.5 to3.0 j/cm². The oscillated laser beam intensity is controlled bydetecting the beam, which has been slightly passed through the mirror36, with a controller 40 and controlling the XeCl laser 35 based on thedetected signal. Whether or not the laser beam is properly irradiated onan intended IC die is determined as follows: the beam from an arc lamp41 is slightly reflected at a half mirror 42 and the thus separated beamis detected with a photodiode 43 and a camera 44, through which the beamis monitored as 45. The signal is transmitted to an XY stage controller46, enabling one to move the XY stage in position. The signals set outabove are inputted to a host computer 47, which control the individualcontrollers and the optical controller 48 to control the optical system37.

When one IC die on the wafer 31 is heated with the laser beam, thefollowing relationships between a beam size, A×B, and an IC die size,a×b, illustrated in FIG. 2 should be satisfied.

    A=a+C×(0.6-0.8)×2 mm

    B=b+C×(0.6-0.8)×2 mm

Wherein C represents a grid line width.

In a subsequent irradiation cycle, the beam should be irradiated on anadjacent IC chip as superposed with the first beam at C×(0.2-0.6) mm.

If a single IC die is to be irradiated, a small size laser sufficientfor usual laser beam irradiation may be used. If the laser has highoutput power, two adjacent IC dies or four IC dies may be thermallytreated by the irradiation at one time. When a number of IC diesarranged as a group in n lines and m rows are heated with a laser beam,the beam size, An×Bm, should satisfy the following relationships.

    An=n×a+(n-1)C+C×(0.6-0.8) 2 mm

    Bm=m×b+(n-1)C+C×(0.6-0.8)×2 mm

wherein C has the same meaning as defined above.

The superposed size of the laser beam with a laser beam applied in asubsequent cycle for another group of the IC chips should likewise be ina range of C×(0.2-0.6) mm.

The aperture 39 of the optical system 37 used for this purpose shouldresemble the shape of the total dies in n lines and m rows.

As is particularly shown in FIG. 1(b), the Al-Si film 18 is metal-flownto fill the contact holes 16 therewith. Thereafter, the film 19 issubjected to patterning in a desired shape according to aphotolithographic technique e.g. a RIE procedures using CF₄ gas.Moreover, the Al-Si film 18 and the Ta-Si film 17 are successivelypatterned, for example, according to the RIE procedure using BCl₃ gas,thereby completing an Al wiring layer or conductor 20.

When the film 19 used as an anti-reflective film is made, for example,of tungsten, it exhibits a very high light absorption coefficient of9×10⁵ cm⁻¹ relative to UV light with a wavelength of 308 nm. Inaddition, as shown in FIG. 3, the light reflectance or reflectivity canbe satisfactorily reduced even when a tungsten film 19 having athickness of approximately 300 angstroms is used for the W/Al-Si/SiO₂/Si structure. This means a high light absorption efficiency of theAl-Si film 18, with the possibility of enlarging the beam size.According to the RBS analysis, when the substrate temperature is 300°C., the W film 19 and the Al-Si film 18 are difficult to react with eachother. The reaction between the W film 19 and the Al-Si film 19 isminimized since the wavelength of the irradiation beam is short and,thus, the depth of transmitted light is at most (several) tens ofangstroms. Moreover, since the wettability of Al on the Ta-Si film 17serving as a barrier metal is good, the flowing of Al is possible at asmall beam energy. Thus, the elements beneath the Ta-Si film 17 aresuppressed from being damaged.

The anti-reflective film 19 is not limited to tungsten. Other metal oralloy films which are difficult to react with Al, such as TiW film, TiNfilm, Ti film, Cu film and Mo film may be used. The Al alloy used as thefilm 18 may be not only Al-Si, but also Al-Si-Cu, Al-Si-Ti and the like.

As will be apparent from the foregoing, since an anti-reflective film isformed on an Al alloy film, the light absorption efficiency of the Alalloy film is improved, making it easy to give a beam size larger than achip size. Moreover, the wafer made of Si is heated at temperatureshigher than the recrystalization temperature of Al, so that the flowingof Al by a relatively small energy is possible. The superposed portionof laser beams which are, respectively, applied to adjacent IC chips isset on the grid line region. This ensures irradiation of the laser beamon the respective IC chips at a uniform intensity. This is advantageousin that the elements including the Al wiring layer are suppressed fromdamaging with a significantly improved yield of IC chips.

Since the anti-reflective film and the Al alloy film are not reactedwith each other, the Al alloy film is protected from deterioration. Theanti-reflective film serves as a protective film of the Al alloy film,the formation of hillocks in the Al alloy film can be prevented, coupledwith an improvement in migration lifetime.

Although the invention has been described in its preferred form with acertain degree of particularity, it is to be understood that manyvariations and changes are possible in the invention without departingfrom the scope thereof.

What is claimed is:
 1. A method for forming an electrode wiring conductor on a semiconductor wafer which comprises the steps of:depositing an intermediate insulating film on portions of the semiconductor wafer and making a contact hole in the intermediate insulating film; depositing an aluminum (Al) alloy film over said contact hole in the intermediate insulating film; forming an anti-reflective film on the Al alloy film, and forming a plurality of IC dies on the semiconductor wafer, the IC dies being separated from one another by a grid line region; successively irradiating one or more of the IC dies on said wafer with a laser beam controlled to have a beam size larger than a die size and to cause a superposed portion of the beam to be set on a grid line region of the semiconductor wafer until the Al alloy film flows, thereby filling said contact hole with the Al alloy film; and selectively etching the anti-reflective film and the Al alloy film successively, thereby forming on said contact hole an Al wiring conductor having the anti-reflective film thereon.
 2. A method according to claim 1, wherein said anti-reflective film is a refractory metal film which is difficult to react with the Al alloy and said refractory metal film is left on said Al alloy film after the selective etching.
 3. A method according to claim 1, wherein said anti-reflective film comprises a member selected from the group consisting of W, TiW, TiN, Ti, Mo and Cu.
 4. A method according to claim 1, wherein said anti-reflective film has a thickness of not less than 20 nm.
 5. A method according to claim 1, further comprising another refractory metal film formed below the Al alloy film.
 6. A method according to claim 5, wherein said another refractory metal film is made of Ta-Si.
 7. A method according to claim 1, wherein the laser beam irradiation is effected in such a way that the semiconductive substrate is heated to a recrystalization temperature of the Al alloy.
 8. A method according to claim 1, wherein said laser beam has a wavelength in a UV light range.
 9. A method according to claim 1, wherein the laser beam irradiation is effected in an inert gas atmosphere.
 10. A method according to claim 1, wherein the laser beam irradiation is effected at a reduced pressure.
 11. A method according to claim 1, further comprising repeating the laser beam irradiation and the selective etching procedures on all the IC dies on the semiconductive wafer, thereby forming an electrode wiring conductor on all of the IC dies.
 12. A method of processing a seimconductor wafer to form electrode wiring conductors on integrated circuit dies on the wafer, the dies being delineated by a grid line region, comprising the steps of:establishing an intermediate insulating film on the wafer and forming a contact hole in said film; establishing an aluminum alloy film over said contact hole; establishing an antireflective film on said alloy film; irradiating one or more of said dies successively with a laser beam controlled to have a beam size larger than the size of a die and causing said beam to set on said grid line region until said alloy film flows to fill said contact hole; and thereafter selectively etching the antireflective film and alloy film to form the elctrode wiring conductors.
 13. The improved method of claim 12 further comprising the step of forming an antireflective film on said alloy film prior to said irradiating step.
 14. An improved method of processing a semiconductor wafer to form electrode wiring conductors on integrated circuit dies on the wafer, comprising the steps of:configuring the dies to be separated by a grid line region of the wafer; establishing an aluminum alloy film upon said dies; and irradiating one or more of said dies successively with a laser beam controlled to have a beam size larger than the size of a die and causing said beam to set on said grid line region until said alloy film flows to fill a contct hole.
 15. The method of claim 14 further comprising the step of forming an antireflective film on said alloy film prior to said irradiating step.
 16. The method of claim 15 further comprising selectively etching said antireflective film and said alloy film.
 17. The method of claim 14 further comprising forming an intermediate insulating film upon portions of said dies, forming a contact hole in said intermediate insulating film;wherein said step of establishing an aluminim alloy film occurs after said step of forming a contact hole, and wherein said aluminum alloy film is established over said contact hole.
 18. The method of claim 16 further comprising forming an intermediate insulating film upon portions of said dies, forming a contact hole in said intermediate insulating film;wherein said step of establishing an aluminim alloy film occurs after said step of forming a contact hole, and wherein said aluminum alloy film is established over said contact hole.
 19. The method of claim 1 wherein said dies are irradiated one by one.
 20. The method of claim 12 wherein said dies are irradiated one by one.
 21. The method of claim 14 wherein said dies are irradiated one by one. 